Today it is widely known that the aeronautics industry requires structures which, on one hand, bear the loads to which they are subjected in order to comply with high strength and rigidity requirements and which, on the other hand, are as lightweight as possible.
These requirements result in the increasingly greater widespread use of composite materials in primary structures since by suitably applying the composite materials, significant weight savings can be achieved with respect to designs with another type of materials, such as metallic materials, for example.
Integrated structures have proven to be very efficient in this sense, integrated structure being understood as that structure in which the different structural elements are manufactured all at once. This involves an additional advantage in the use of the composite materials because since they are formed by independent layers, they can be gradually stacked on one another in various shapes and orientations to form the desired structure.
This also entails the advantage of a reduced number of parts to be assembled, which means essential cost savings for competing on the market.
Generally, the mentioned structures usually consist of a skin with integrated stringers, glued or cured together, normally arranged longitudinally with respect to the skin to enable reducing its thickness and making it competitive with respect to weight without this jeopardizing the mechanical properties of the assembly.
This assembly formed by the skin plus the stringers can be manufactured in a single manufacturing process which, generally speaking, comprises the following steps:                Stacking the layers of composite material on a base;        Folding to form the parts into the desired shape;        Superimposing layers of composite material in a pre-impregnated state, such that it allows rolling and forming without producing fiber distortions or creases, and such that it allows the ultimately cured part to not have permanent deformations due to thermal stresses;        Placing in the curing tool; and finally        Curing the complete structure by applying a single pressure and temperature cycle.        
In the current state of the art, the mentioned part curing process involves using high-temperature (more than 180° C.) and high-pressure (more than 10 bar relative pressure) heating cycles. To that end, the use of autoclaves is known, particularly in the field of aviation, in which the autoclaves are accordingly quite large.
However, the high temperatures and pressures to which these parts are subjected inside the autoclave result in the occurrence of the risk of deflagration caused by the presence of volatile compounds generated during the polymerization process of the resins making up the part to be cured.
This problem is sometimes solved by using anti-deflagration autoclaves designed such that their casing is robust enough so as to withstand an internal gas explosion without sustaining damage and of placing anti-deflagration openings consisting of flange joints, for example, so that the flame cannot propagate to the outside atmosphere.
This solution, however, entails a significantly higher autoclave price, so such autoclaves are not applicable in the field of aeronautics where a large size is required. Furthermore, the use of the system does not prevent deflagration, but rather controls its effects, so both the part being cured and the pieces of equipment, tools, etc., would continue to be produced, which is something to be avoided at any cost in this field due to high material and labor costs.
Another solution known in the state of the art to prevent deflagrations inside autoclaves or any enclosure is to make the inner atmosphere thereof inert by high-pressure injection of inert gases such as molecular nitrogen, carbon dioxide, etc., reducing the amount of oxygen and therefore stopping combustion. In the case of autoclaves, such gases do not provide any benefit/cause any harm to the process since they do not confer any additional quality or property to the part, but due to the low proportion of oxygen in the inner atmosphere, they do assure that flame propagation does not occur in the event that the combination of high temperatures, high pressures and a release of volatile substances may provoke same.
Therefore, taking advantage of the fact that it is necessary to maintain high pressure inside the autoclave for correctly performing the curing process, the pressure is achieved by injecting that inert gas, typically nitrogen, which is abundant in nature and non-toxic and on the other hand creates the inert atmosphere preventing deflagrations from occurring.
However, these inerting systems using nitrogen have the drawback of the substantial environmental impact involved due to the high electrical power needs required for generating same every time the system is used, since the gas used for pressurization and for creating the inert atmosphere is lost upon opening the chamber if there are no recovery systems, something that tends to occur in those installations with a single autoclave. On the other hand, in manufacturing plants where there are several autoclaves and a nitrogen recovery system is implemented, it would nonetheless have to be taken into account that prior gas storage in cylinders or containers also involves a high financial cost and greater installation complexity.
Finally, another drawback of these systems in which the inside of the autoclave is made inert using nitrogen is that for the inert atmosphere created to be effective, the gas must be homogenously distributed inside the autoclave, which also involves an additional problem as it will make installing auxiliary forced ventilation systems homogeneously distributing the gas necessary. All this evidently has an impact on the final price of the parts obtained by this system, and therefore results in a loss of competitiveness.
A system for making an autoclave inert that is fast and effective enough so as to prevent deflagration that damages the part, tool or the autoclave itself, while at the same time minimizing the amount of gas to be used and simplifying the structure of the assembly so that the cost for curing parts is competitive, is therefore necessary in the state of the art.